This invention relates to a forming tool made from resins and fillers for the cold forming of sheet metal. It is especially suitable for forming short runs of sheet metal parts with drop hammers, hydraulic presses or mechanical crank presses.
More specifically, the forming tool described herein provides for a lightweight replacement to the traditional kirksite or aluminum dies used for forming short runs of sheet metal parts.
Traditional methods for making short run dies not only involve the use of heavy materials, but necessarily involve lengthy procedures to make the dies.
Attempts to use a substitute for the traditional methods have employed laminates coupled with cores of epoxy resin blended with various aggregates, such as aluminum, crushed rock or other inorganic materials.
This type of die construction has mostly been used for vacuum forming molds, prototype injection dies and limited run compression mold dies. However, the successful application of this process in a heavy environment, such as the automotive industry, has generally been unsuccessful. A description of some of the uses of plastic tools and their methods of fabrication is contained in the proceedings published as a result of the "Tenth Annual Seminar On Plastics for Tooling" given at Purdue University on June 12th and 13th, 1968; more specifically, an article by L. E. Winter entitled "Types of Plastic Tools and Methods of Fabrication" which can be found on page 65 of the proceedings of the tenth annual seminar. Also of interest is U.S. Pat. No. 4,125,351 to Alfter, et al.
It has been discovered that the element of the plastic tool which is most critical is the aggregate employed in the reinforcement core of the laminated die. Different aggregates have been employed ranging from popped popcorn to gravel. The discovery of an ideal material for a heavy-duty industrial purpose plastic tool has gone undetected for many years. Recently, a lightweight slag was used as an aggregate in the abovedescribed process. The slag is a by-product of making steel and is a combination of silica, aluminum oxide, and lime. During the steel making process, the slag exists as a white frothy hot fluid and the particular slag employed in the subject process is formed by forcing air into the fluid slag to cool it. In addition to cooling the fluid slag, the air shapes the slag into aggregate. The aggregate formed is irregular in shape and usually contains at least one air pocket or void.
Utilization of this lightweight, inexpensive, porous, and strong byproduct of the steel making process is the key to successful use of plastic tool forms in a heavy environment such as the short run of prototype automotive sheet metal parts.